Transmission circuits



1ine when the other line is in nee.

P.tentecl Dec. 19, 1933 OFFIC snmusmsszes omcnrrs Harold M. Pruden,Maplewsd, N. "J., and Paul W. Wasworth Elmhurst, N. 15., assignors toIncerporated,

New Yerk, N. Y., 2, corpcrationof New York Application December 23 193Serial Nc. 648,680

6 Claims.

This invention relates to the transmissioh of inteligence by means ofe1ectrie waVes and more especialiy te such systems invelving two-waycommunicatcn, in which the wave s ef the same frequency range arepresent in each oneway path.

In two-way transmission systems involving closely related frequencies,tieuble has arisen from whathas ceme to be known as snging, that is, smeof the transmitted waves are 1eturned to the receving circ1iitand thesystem as awhole tends te become an oseillator.

1Another source of trouble is due to refiection currents known asechoes. This is closeiy allied to the singing dificulty. T0 obviate suchtroubles it has become necessary to disable ons Because" of thenecessity of disabling one transmission 1ne when the second line istransmitting signals, a further difliculty is met due to thecomparatively longtime nvolved in transniitting the signals fr0m onesubscriber at one end of the system to the other subscriber at the otherend of the system. A seri0us iesu1t of the long time of transmissionover such a systerri is the increased chance that the two subscribers atthe ends of the system wll both start talking within the time intervalequal to the tota1 time of transmission over the system. Each subscribertherefore obtains control of the signal cont1ei apparatus at his end fthesystem for transmitting andfor blocking out the signals receivediremthe ether subscriber. Neither subscribe1 aan then hear the other;

-T0 invercome the difiicultes mentioned, considerable apparatus hasheretcfore been used. The present invention has for an abject theimprevement of two-way communication systems of the general typesindicated.

LA specific object of this invention is the supp1essi0n of singing andechoes in twoway communication systems.

These and ether objects of the invention have been accempiished and atthe same time the circuits invelved have been greaty simpliiied by thearrangement to be decribed in connectien with the attached drawing,which represents schematcally ons f01n1 WhC11 the inventcn may take.

Refezrng n0w te the srawing, line 1 represents a tWo-wire line leacinggenerallyrom a telephone switchboard, sub-scribe1g etc. which terminatesin the usua'i hybridcc esnnestion 3 and terminating netwerk 1. A twowire line 5 is adapted te transmit in the directioncf the arrowassociated therewth, which diiectien will be referred to as occasioniequires as from west to "sary toshow them in detail.

east. Line.5 wil1 tlierefore be known as the transmit 01" west line.

A second two-wire line6 is adapted te transmit in the direction f thearrow associated themwith. This 1ine wi1l therefore be referred t as thereceive or cast line.

Lines 5 and 6 may 1ead to a radio transmitter ancl receiver,'respectively, or to the tenninating equipment of a submarine cable,etc.

Line 5 is equpped with an aniplifier 7, preferably of thespacedisehargetype and a delay filter 8. Amplifiers and filtersof the typeused are so well known that it is not deemed neces- A syllabicamplifier-detector 9 is connected in shunt te line 5 and is adapted tohave impressed upon it a small amount of the electric wave energypresent in lne 5. The output of this amplifier-detector is impressedupona filter 10, "the output ofwhich is again impressed on transmlttingmaster po1ar relays 11 and 12. A third transmitting master p0lar re1ay13 is connected in the anode circuit of amplifier-detector 9.

Reays 11 and 12 are connected in series in respectviy reverse order inthe output of filter 10, which filter may have a cut-off frequency fabout 20 cycles per second. With the amplifier-detector and filterarrangement shown, it is found that there is produced in the output ofthe filter a current in one direction at the beginning of a syllableand. a current in the opposite direction at the end of a syllable.During the nermal speechtherefore the armature of reays 11 and 12continue to vibrate.

Relay 13 is csnnected in the output amplifierdetector 9 and itsarmatureis nermally attracted. The function of this relay is to perate (releaseits armature) in case of along wave train of suflicieht amplitude and.thus to bridge the interi al between the eperation of re1ays 11 and 12.

Amplifier-deteetor 9 is of the type in which the space current isdecreased below the normal 'va1 ue when waves are incident upon itsinput circuit. Whensufiiciently streng waves are im pressed enamp1ifier-fletector 9 and persist for a sufciently long time, relay 13releases due to the decrease in spacecurrent. The acton ofamplifierdetector 9, filter 10 and relays 11, 12 and13 are described insomewhat more detail in the copending application of H. J. Fisher,Se1ial No. 578,350, filed Decemberl, 1931.

Relays 1.1, 12and 13 are equipped with biasing Wndings distinctfromtheir operate windings, which are energized from battery 14 asshown.The eurrent through these bias Windings opposes the action of thecurrent in the operate windings and hence opposes false operation ofthese reiays.

Relaysl5, 16 and 17 are controlled as to operation by the operation ofany one of relays 11, 12 and 13, as-.will appear hereinafter. Relays 15,16 and17 also are provided with biasing windings in series. Reiay 17o'stains its biasing current from battery 18, relay 16 from batteries 18and 19 and re1ay 15 from batteries 18, 19 and 20. If desired, only onebattery may beused and the circuit wil1 in suchcase contain resistancesof different vaiues so that the biasing currents through these reiaysdiifer. Forthe best operation of the circuit, it is desirable that re1ay15 have the strongest bias while relays 16 and 17 is independentlybiased by current frombatter5w 26.

Relays 27, 23 and 29 are associated with the main receivingamplifier-detector 34. These relays are also provided with biasngwindings, that of re1ay 27 being supp1iedindependently from battery 30,while basing wiridings of relays 28 and 29 are supplied by batteres 31and 32.

. The auxiliary receiving ampiifier-detector 33 is shunted across thereceive line 6, which line is also provided witha norn1ally closedswitch consistingof the armature and associated contact of relay 17,termination netwerk 3 and 1 and a series amplifier 35.

The operation of the system is as follows:

Signals incoming from line 1 after passing through hybrid coil 3 areamplified ioyampiifier 7. Some of the amplified energy is applied tosyllabic amplifier-detector 9, while the main portion of the energy isretarded by de1ay filter 8. The short-circuit across the line,consisting of armature and associated contact of relay 15, will keep themain portion of the energy from passing a1ong over line 5 un1ess it isopened. The signals or speech wavesimpressed on the syllabicamplifier-detector 9 are not a long continuous wave train, but occur asshort trains of waves of syllabic duration. The syilables or vocalintervals occur at the rate of 2 to 20 cycles per second. It isiound, aspointed out above, When speech waves are rectified, as byamplifier-detector 9, and. are passed on through the output transformerof the amplifier and low-pass filter such as 10, that they produc in theoutput of the filter a current impuise of one sign at the beginning of asyllable and another current im pulse of opposite polarity at the end ofa syllable.

Re1ay 11 is arranged te attract its armature upon the initial impuise ofa syllab1e while relay 12 attracts its armature on the final impulse ofasyllable. A succession of short syllables there forehas the eect ofkeeping the armatures of relays 11 and 12 in a state of vibration.

In the case of a long sustained speech sound or of a tone which may beapplied to the system for testing or other purposes, relavs 11 and 12would not be caused to vibrate continuously.

' Reiay 11 would operateupon the beginning of foliowing manner: As soonas the armature of such a long wave train, but wou1d then release itsarmature and .re1ay 12 would not operate until the end of such a wavetrain. The func tien of relay 13 is to operate in case of a long wavetrain of suficient amplitude and ths to bridgeover the interval betweenthe operation of reiays 11 and 12. The bias winding of re1ay 13 causesthis re1ay to be sluggish in its action and also to require apredetermined current to cause its operation so that it will not beoperated bythe relativeiy weakcontinuous noise currents which may bepresent on the system.

As stated, ampiifier-detector 9 is of the type in which the spacecurrent is decreased below normal value When waves are incident upon itsinput circuit. Re1ay 13 is shown with its armature normally attracted.When suflicintly streng waves are impressed on amplifier-detector 9 andpersist for a sufciently long time re1ay 13 releases due to the decreasein space current.

When re1ay 11 operates to shift its armature from the normai positionshown in the drawing to the opposite contact, the train of relays 15, 16and 17 are energized. This takes place in the relay 11 leaves its normalcontact, a rush of current is ailowed to flow from battery 36, contactand armature of relay 22, conductor 37, contact and armature of relay29, conductor 38, resistance 39, condens-er 16 and the operate :windingsof relays 15, 16 and 17 in series." This charging current of thecondenser0 causes these relays to operate quickly. Whenth armature ofrelay 11 reaches its opposite or front contact, re1ays 15, 16 and 17 aremaintained operated bythe direct current from battery 36throughthearmatures and contacts of re1ays 11,"12 andl3.

When at the end of a syliab1e relay 12 attracts its armature, the sameoperation occurs as was just described for relay 11. By thejoperatiohofrelays 11 and 12 as described relays 15, 16 and 17are maintainedoperated as;long asspeech currents come in over line 1. The condenser 40in themanner that has been described. causesj quicker operationof re1ays15, 16 and 17 and hence requires less de1ay of the signal currents inde1ay filter 8. The unctionof re1ay13 has been described and itsoperation and its effect upon re1ays 15, 16 and 17 is identcal with thatof relays 11 and 12.

The release of all three reiays 11, 12 and 13 breaks the dischargecircuit for condenser 40 (prior to the release ofre1ay 16) and the condenser is aliowed to charge in series withthe windings of relays 15, 16and17, armatures and rest contacts of re1ays 22 and 29 and battery 36preventing their release immediately.

As the charging current of condenser 40decreases, the biasing currentsbegin te overcome the operate or condenser current and, in ac cordancewith the strength of the bias currents, relay15 releases first and. thenrelay 16, after which relay17 releases. When re1ay 16 releases, itcloses at its back contact a connection to ground from condenser 40,causing the condenser todischarge through the windings of "relaysij 15,16 and 17 in the opposite direction to the operate current, but sincethese relays are of poiarized type, they are not operated by thiscurrent and the circuit is returried to normal condition.

As a result of the chainof operations described, as soon as signals orspeech waves come in over line 1, relay 15 operates to clear line 5 andallow speech to proceed While relair 17 opens line 6 at 150 its armatureand associated contact. These condtions are maintained as long asspeechcontinues in line 5. At the cessa;tion of speech, these relays arereleased in the sequence notedafter a suitabl hangover time, which iscontroiled by the strength of their respective biasing currents and thishangover time is made long enough to allow for alithe speech to pass onthrough line 5 and to prevent echoes or other disturbances in 1ine 6.

In the description which foliows and whch is directed to the feature ofreducing the chance of 1ock-out asbetween subscribers startingto talkWithin the time interval of the transmission time of the system, itshould be home in rnind that at the cast terrninalof ;the radio 01 cabielink there is an equipment simiiar to that which has been described forthe west terminah At the west terminal there is bridged across the line6 2.11 auxiliary receiver-ampiifier-detector 33 ahead of the disabiingswitch which is controiled by the armature and associated contact ofre1ay 17. The output of this auxiiiary ampiifier-detector includes thewinding of aux- 1iary master relay23, which reiay has a hiasing winding,the current for which is suppiied by battery 26.

When on reoeipt of: speech energy in line 6 the armature of reiay 23leaves its back contact, there is a rush of current from battery 41 techarge condenser 42. This current passes through the operate windings ofre1ays 21 and 22, causing these relays to operate quickly.

When the armature of re1ay 23 makes contact with the front contact,direct current rom battery 11 passes through the 'same winding of relays21 and 22 and maintains them operated. Upon operation, the armature ofre1ay 22 breaks contact with its back contact, thereby opening thecircuit from battery 36, so that no current can flow therethrough toenergi"e reiays 15, 16 and 17. Hence, the short circuit cannot beremoved from line 5 by re1ay 15, nor can line 6 be opened by theoperation of reiay 17.

Speech waves and signa1s may then pass along line 6 through ampiifier35, hybrid coils 3, etc. to line 1 andthe other subscriber. 'Energypassing a1ong line 6 is impressed on amplifier-detcctor 34, the outputof which inciudes the operate winding of master re1ay 27.

Re1ay 27 upon operating causes the operation of relays 28 and 29 in thesame rnanner as relay 23 causes the operation of reiays 21 and 2. Thatis, when the armature of reia7 27 leaves its back contact, a rush ofcharging current for condenser 43 from battery 44 causes the quickoperatich of reiays 28 and 29. When the armature of re1ay 27 makescontact with its front contact, there is a direct current fiow frcmbattery "i1 through the operatewindings of reiays 23, 29 to maintainthem operated as long as reiay 27 is operated; The armature of relay 29upon operating also opens the energizing circuit of re1ays 15, 16 and17.

It is therefore obvious thatif signal waves the east reachampiifierdetector 33, these iatter materially reduced since in order forlook-out -to occur the second subscribermust starttalking after thefirst subscriber has started within the time interval of thetransmission time between terminals.

Upon the ccssation of signai waves in line 6 and the consequentdeenergization of relay 23,

relays 22 and 21 drop of! in sequence dependent upon their biasingcurrents. The same operation occurs in conhection with relays 27, 28 and29. Relays 29 and 22 are adjusted to havesuflicient hangovertimefor a1ispeech to clear.

It isto be understood that auxiiiary receiver ampiifier detector 33 isless sensitive than the main ampiifier detector 31. If this were notsonoise currents incoming over line 6 might cause the operation of reay 23and the subsequent disabing or" transmitting line 5, cutting oi theoutgoing speech. However, with the sensitivityadjustrnent as stated,noise currents are ineifective to disable iine 6, het stiii the distanttalkers speech, at least some of the strenger impulses of it, is able tooperate re1ay 23 and thus obtain control of the circuit. If the initialweak por-, 105 tiens are lost this is of no consequence since there isassumed te te outgoing speech on circuit 5at this time and the taikerproducing that speech would be unable to catch the initial weak soundsof the distant talkcr anyway.

Many changes may, of course, be made in the circuits disclosed whi1estili retaining the features of simplicity of circuit arrangement,positive and fast operation and release characteristics provided by theinvention as defined in the appended 115 claims. It is further to beunderstood that in order to simplify the description and drawingindividual batteries have neen shown for the operating and biasingcurrents but that in actua operation a single battery may be used.

hat is ciaimed is: 1. In combination, voice-operated relays,

switching re1ays, each of said switching relays being provided with abias winding and an operate winding, a condenser, a source of current,an armaturc and a front and a back contact associated with each of saidvoice-operated reiays, a circuit comprising said condenser, said sourceof current and the armatures and contacts of said voce operated re1ayswhereby when an armature leaves its back contact charging current iscaused to flow through said condenser and. through the operate windingsof said switching relays and when said armature makes contact with itsfront contact current passes through said operate windings te rnaintainsaid switching relays operated.

2. A combination in accordance with claim 1, characterized in this thatindividual means are providcd to regulate the fiow o current throughsaid bias windings.

3. A combination in accordance with claim 1, charactcrized in this thatwhen the armature of said voce-operated reiay ieaves its -front contactto open the circuit through the operate windings of. said switchingrelays, said switching re iays become deenergized in a sequence inaccordance with the current flow through the individual bias windings.

4. In combination,

voice-operated rlays,

windings.

switchirig relays controlled thereby, biasing windings on a1l saidrelays, a condenser, cunent means in circuit with said condenser andsaid. re1ays whereby operaticn of said voice operated relays causes asudden flow of 0pe1ating current in the condenser circuit and throughsaid switching relays, whch switching relays release upon the decline ofoperatng current in a sequence dependent upon the current through theirbiasng 5. In combination, voice-operated relays, swtching relayscontrolled thereby, saidswitchng relays being provided with a biaswndingand an operate winding, a source of current, said source ofcurrent beingconnected t0 said bias windings, indvidual means associated with saidbias windings to control the amount of c11rrent flow therethrough, a.condenser associated with the operate windings of said switchingrelays,coh-

tact means associated with said voice-operated.

relays, the opening of which causes charging current to flow throughsaid condenser and thro ugh sad operate windings of sad swtching relaysin series, causing said relays to operate and ether contact meansassocated with said switching re- 1ayS which open upon opration of said.switching relays which 1atter contact means upon closure,

when the circuit releases, cause said condenser to discharge with theattendant discharge current flowng through the operate windings of saidswitching relays in the opposite direction to that of said condensercharging current to through said condenser and through the wind ing ofsaid switching relay and when said armature makes contact with itsfrontcontact a. circuit is closed. rom saic'l source of current through thewinding of said switching relay.

HAROLD M. PRUDEN.

PAUL W. WADSWORTH.

